Environmental parameters that determine distribution coefficients of radionuclides for repositories


Environmental parameters that determine distribution coefficients of radionuclides for repositories

Stockmann, M.; Brendler, V.; Richter, C.; Flügge, J.; Britz, S.; Noseck, U.

In order to treat radionuclide sorption processes in natural systems more realistically, temporally and spatially variable distribution coefficients (smart Kd values) are calculated as a function of important environmental parameters such as pH, ionic strength (IS), concentration of dissolved inorganic carbon [DIC], calcium [Ca] and radionuclides [RN]. This smart Kd concept is implemented into the transport code r³t [1].
As a test of the modified code r³t and sensitivity analysis of radionuclide sorption regarding the mentioned environmental parameters, a possible future climate transition (seawater transgression) at Gorleben site / Germany was modelled [2]. Seawater inundation drastically influences the distribution and values of all environmental parameters. Chemical changes cause dissolution or precipitation of calcite and these in turn affect the pH, DIC and Ca concentration. In consequence the Kd values and therewith the transport of radionuclides is impacted.
The results of the calculations are plausible: environ-mental parameters follow expected trends and major dependencies. As a consequence of the low Ca and DIC concentration in seawater, calcite dissolves in the aquifer and causes an increase of the pH. The Kd values change according to the changes in environmental parameters. The pH has the most dominant impact on the smart Kd values for most of the considered RNs, except for Pu and Th, for which the DIC concentration has the strongest impact. Under the assessed conditions for seawater transgressions the smart Kd values of Cs, Ni, Am and Np(V) increase, those of Se(VI) and U(VI) decrease with increasing pH. The smart Kd value particularly of Pu and Th decreases with increasing DIC concentration.

  • Poster
    Goldschmidt 2013, 25.-30.08.2013, Florence, Italy

Permalink: https://www.hzdr.de/publications/Publ-18644
Publ.-Id: 18644